Final answer:
Higher RBC counts in males are primarily caused by the expression of androgens, which stimulate RBC production.
Step-by-step explanation:
The cause for higher red blood cell (RBC) counts in males compared to females is attributed to the expression of androgens. Androgens are male sex hormones, which include testosterone, and play a pivotal role in stimulating the production of RBCs. This is partly why males tend to have higher hematocrit levels compared to females. The hormone erythropoietin (EPO) also influences RBC production, which is secreted in response to low oxygen levels and triggers the bone marrow to produce red blood cells, further influencing overall RBC counts.